Imprint lithography has emerged in various forms as a potential alternative to conventional photolithography because of its ability to print smaller features at low cost. Step and flash imprint lithography (SFIL) is a variant of imprint lithography that is amenable to the resolution and overlay requirements necessary for the fabrication of advanced semiconductor devices. In SFIL, a low-viscosity photosensitive molding material is molded between a mechanically rigid template having a relief pattern and a substrate and then is exposed to actinic radiation. The resulting hardened layer, having a three dimensional pattern, can be used as an etch mask to transfer the imprinted pattern into the substrate below.
To form an effective etch mask with nanoscale features, it is often desirable to form patterned features with a large height-to-width aspect ratio. Fabricating templates and producing imprints with such aspect ratios, however, can range from extremely challenging to impossible, especially as the imprinted features approach nanometer-scale dimensions. To alleviate this problem, in SFIL, a so-called bilayer etch mask approach is employed. In this approach a silicon-containing organic material is imprinted on an underlying silicon-free organic layer that covers the substrate of interest. Because organic materials can be anisotropically plasma-etched in a highly selective manner with respect to silicon-containing organic materials, the imprinted pattern can be transferred into the underlying transfer layer to form high-aspect ratio features that can be used as an etch mask to transfer the imprinted pattern into the substrate.
Unfortunately, imprint lithography intrinsically possesses a characteristic that complicates the process just described. When producing an imprint, the molding or imprint material cannot be fully excluded between the template and the substrate. As a result, a hardened layer, called the residual layer, remains between the imprinted features. To effectively transfer the imprinted pattern into the underlying transfer layer, the residual layer must be removed. Removing the residual layer inevitably alters or damages the shape and/or the size of the imprinted features. This problem worsens as the thickness or uniformity variations of the residual layer approaches or exceeds the height of the imprinted features.
To minimize these problems associated with the residual layer, a so-called reverse-tone SFIL (SFIL-R) process was developed. In the SFIL-R approach, a non-silicon containing organic material is imprinted over a non-silicon containing organic transfer layer. After all the imprints on the substrate have been produced, the substrate is coated and cured with a silicon-containing material that ideally forms a planar surface over the imprint topography. Using plasma etch techniques and chemistries known in the art, the thickness of this silicon-containing planarizing overcoat is reduced until the tops of the imprinted features are exposed. Again, because organic materials can be anisotropically plasma-etched in a highly selective manner with respect to silicon-containing organic materials, the non-silicon containing imprinted features can be selectively removed along with the non-silicon containing transfer layer material directly beneath them. The remaining pattern, which now has the opposite or reverse tone of the originally imprinted pattern, can serve as an etch mask to transfer this reverse tone pattern into the substrate.
In current practice, current SFIL-R formulations and processes are sensitive to the presence oxygen, have relatively low curing rates, high volatility, high viscosity, and low tensile strength, which can adversely affect the quality of the imprint mask. In light of these potential disadvantages, there is a need in the art for alternative SFIL-R formulations and SFIL-R processes that are less sensitive to the presence oxygen, have relatively high curing rates, low volatility, low viscosity and high tensile strength.